Grooming multicast traffic in flexible optical wavelength division multiplexing WDM networks

ABSTRACT

There is provided a distance-adaptive and fragmentation-aware all-optical traffic grooming (DFG) method, which addresses the all-optical traffic grooming problem while considering the transmission reach constraints. The DFG procedure provisions traffic demands in optical channels such that the spectrum requires for guard bands is minimized. The DFG procedure provisions optical channels such that network fragmentation is minimized while ensuring the transmission reach constrains over flexible-grid WDM networks.

RELATED APPLICATION INFORMATION

This application claims priority to provisional application Ser. No.61/935,443 filed on Feb. 4, 2014, entitled “Distance-Adaptive andFragmentation-Aware All Optical Traffic Grooming Procedure in FlexibleGrid WDM Networks”, the contents thereof are incorporated herein byreference.

BACKGROUND

The present invention relates optical communications, and, moreparticularly, to distance-adaptive and fragmentation-aware all opticaltraffic grooming procedure in flexible grid wavelength divisionmultiplexing WDM networks.

The following background documents are discussed in the presentapplication:

-   [ITU-T] ITU-T G.694.1, “Spectral grids for WDM applications: DWDM    frequency grid,” May 2002.-   [SGringeri] S. Gringeri, B. Basch, V. Shukla, R. Egorov, and T. J.    Xia, “Flexible Architectures for Optical Transport Nodes and    Networks,” IEEE Communication Magazine, pp. 40-50, July 2010.-   [M.Jinno] M. Jinno, H. Takara, B. Kozicki, Y. Tsukishima, Y. Sone,    and S. Matsuoka, “Spectrum-Efficient and Scalable Elastic Optical    Path Network: Architecture, Benefits, and Enabling Technologies,”    IEEE Communication Magazine, pp. 66-73, November 2009.-   [APatel1] A. N. Patel, P. N. Ji, J. P. Jue, and T. Wang, “Routing,    Wavelength Assignment, and Spectrum Allocation in Transparent    Flexible Optical WDM (FWDM) Networks,” Proceeding of OSA Photonics    in Switching, PDPWG1, July 2010-   [GZhang] G. Zhang, M. D. Leenheer, and B. Mukherjee, “Optical    Grooming in OFDM-Based Elastic Optical Networks,” Proceeding of    OFCNFOEC, no. OTh1A.1, March 2012.-   [APatel2] A. N. Patel, P. N. Ji, T. Wang, and J. P. Jue,    “Optical-Layer Traffic Grooming in Flexible Grid WDM Networks,”    Proceeding of IEEE GLOBECOM, December 2011.-   [APatel3] A. N. Patel, P. N. Ji, J. P. Jue, and T. Wang,    “Defragmentation of Transparent Flexible Optical WDM (FWDM)    Networks,” Proceeding of OFCNFOEC, no. OTuI8, March 2011.

In the ITU-T standardized fixed grid networks [ITU-T], fixed amount ofspectrum (50 GHz) is allocated to every channel irrespective of theoperating line rate, and the center frequency of a channel remains fixed(FIG. 1(a)). Such a fixed channel grid may not be sufficient to supportimmerging super-channels which operates at 400 Gb/s or 1 Tb/s linerates. For example, 50 GHz of spectrum is not sufficient for 400 Gb/sand 1 Tb/s channels which require 75 GHz and 150 GHz [SGringeri] ofspectrum respectively. On the other hand, supporting such super-channelsby increasing the channel spacing in fixed grid networks may notoptimize the spectrum allocation for channels operating at lower linerates. For example, 10 Gb/s channel requires only 25 GHz of spectrum.Thus, no single fixed channel grid is optimal for all line rates.

There has been growing research on optical WDM systems that are notlimited to fixed ITU-T channel grid, but offers flexible channel grid toincrease spectral efficiency [MJinno]. We refer to such gridlessnetworks as Flexible Grid WDM Networks. In such networks, flexibleamount of spectrum is allocated to each channel, and the channel centerfrequency may not be fixed (FIG. 1(b)). Thus, while establishing achannel in flexible grid networks, control plane must follow (1) therequirement of having the same operating wavelength on all fibers alongthe route of a channel which is referred to as the wavelength continuityconstraint, (2) the requirement of allocating the same amount ofspectrum on all fibers along the route of a channel which is referred toas the spectral continuity constraint, and (3) the requirement ofallocating non-overlapping spectrum with the neighboring channels in thefiber which is referred to as the spectral conflict constraint. Theproblem of finding a channel satisfying these constraints is referred toas the routing, wavelength assignment, and spectrum allocation (RWSA)problem [APatel1].

FIG. 1 shows a comparison of (a) fixed grid WDM network and (b) FlexibleWDM network. Flexible grid networks remove the fixed channel gridrestriction and allow non-uniform and dynamic allocation of spectrum.Channels with finer granularity line rates can be supported by usingOrthogonal Frequency Division Multiplexing (OFDM) modulation scheme withvariable subcarrier assignment. Such channels are referred to asflexible channels. In spite of a flexible spectrum allocation, thespectral utilization of channels may be limited if the network supportsa discrete sets of line rates. Additionally, there is still arequirement of allocating guard bands between channels in order to avoidinter-channel interferences. The total required spectrum for guard bandsincreases in proportion to the number of multiplexed channels in afiber. For example, supporting 10 individual connections demanding 10Gb/s line rates per connection using 10 of the 10 Gb/s flexible channelsallocate 10 times more spectrum for guard bands compared to supportingthe same amount of traffic using a single 100 Gb/s channels andaggregating all connections in a single channel. An effective solutionto improve the utilization of flexible channels. To reduce wastedspectrum in terms of guard bands is to aggregate low speed connectionsonto high capacity channels. Such functionality is referred to astraffic grooming. Thus, by aggregating low rate connections onto highrate channels, traffic grooming improves the bandwidth utilization ofWDM channels, and by reducing the number of multiplexed channels in thefiber, traffic grooming improves the spectral utilization.

Conventionally, traffic grooming operations are performed at anelectrical layer. In electrical traffic grooming, WDM spectrum at theincoming ports are first demultiplexed into individual wavelengthchannels using bandwidth variable demultiplexer. Channels carryingtransit traffic are switched all-optically using an opticalcross-connect (OXC). Low speed connections in the wavelength channelsare aggregated, separated, and switched using an electrical switchfabric that is capable of TDM circuit switching or packet switching byconverting input optical signals into electrical signals using bandwidthvariable (BV) transponders. Finally, the groomed electrical traffic isconverted back to optical signals using variable rate transponders.Thus, electrical traffic grooming improves the utilization of bandwidthand spectral resources of a network; however, this approach is verycostly due to the requirement of additional transponders, and powerhungry due to Optical-Electrical-Optical (OEO) conversions of WDMchannels.

Recently, in [GZhang], the concept of all-optical traffic grooming isproposed in which connections are supported over optical subcarriers,and these optical subcarriers are optically groomed into the sameoptical channel (also referred to as optical tunnel) that is originatedfrom the same source (bandwidth variable transponder) without guardbands. Traffic demands between the same source and differentdestinations can be supported as a single optical tunnel using bandwidthvariable (BV) OXCs. A subset of subcarriers in this optical tunnel canbe dropped at an intermediate node or switched over other routes.However, when switching a subset of subcarriers, guard bands must beallocated at both sides of this set of subcarriers for subsequentswitching in the network. This added guard band is used to avoidinter-channel interference since it is difficult to maintainorthogonality between subcarriers those are generated from differenttransponders, and thus, in all-optical traffic grooming, only sourcegrooming is considered. All-optical traffic grooming is illustrated inFIG. 2 [GZhang]. As shown in Figure, an optical tunnel is established atnode a that carries optical connections for node b, node e, and node d.Optical subcarriers for node b are dropped at node b, while opticalsubcarriers for node d and node e are switched at node c using BV-OXCs.After switching a subset of subcarriers, guard bands are added to theboth sides of this set of subcarriers.

One of the control plane issues in all-optical traffic grooming is: fora given configuration of the optical network in terms of the locationsof optical nodes and deployed fibers connecting optical nodes, thespectral capacity of a fiber link, bandwidth variable (BV) transponderswith the maximum transmission capacity, a set of offered modulationformats offered by a BV transponder, the spectral efficiency andtransmission reach limit of each modulation format, the requiredspectrum of a guard band, and a set of traffic demands, where eachtraffic demand requests a finite data rate between a source node and adestination node, the problem is how to support traffic demands withoptical subcarriers, how to aggregate all optical subcarriers intooptical channels (optical tunnels), how to route optical channels overthe network, how to assign wavelength, and allocate spectrum to theseoptical channels such that the maximum requires spectrum in the networkis minimized. Together the problem is referred to as all-optical trafficgrooming problem in flexible grid WDM networks.

While establishing optical channels in flexible grid networks, someadditional constraints, such as (1) spectral continuity constraint,which is defined as the allocation of same amount of spectrum on alllinks along the route, and (2) spectral conflict constraint, which isdefined as a non-overlapping spectrum allocation to neighboring channelsrouted though the same fiber, must be maintained in addition to theconventional wavelength continuity constraint, which is defined as theallocation of the same wavelength on all links along the route of achannel.

In [APatel2], the authors introduce the concept of optical-layer trafficgrooming in which the grooming operations, add, drop, and switch, areperformed at the radio frequency (RF) layer after OEO conversions ofoptical channels. While all-optical traffic grooming is performedwithout OEO conversions of optical channels. Since the optical-layertraffic grooming approach can aggregate subcarriers originated fromdifferent BV-transponders onto the same optical channels, the controlplane solution of the optical-layer traffic grooming cannot beapplicable to the all-optical traffic grooming problem.

In [GZhang], the authors propose the first solution, Least SpectrumGrooming (LSG) procedure, for all-optical traffic grooming. However, thesolution does not take into account the transmission reach orientedconstraints.

Accordingly, there is a need for a distance-adaptive andfragmentation-aware all optical traffic grooming capability in flexiblegrid wavelength division multiplexing WDM networks.

SUMMARY OF THE INVENTION

A computer implemented method for performing all optical trafficgrooming in an optical network, including providing distance-adaptiveand fragmentation-aware all-optical traffic grooming that enablesall-optical traffic grooming responsive to provisioning of trafficdemands in optical channels such that the spectrum required for guardbands is minimized, such that network fragmentation is minimized whileensuring transmission limits over flexible-grid wavelength0-divisionmultiplexed WDM networks are reached, the providing includes routing agroomed channel, selecting a modulation format for the groomed channel,selecting traffic demands to be aggregated in the groomed channel; anddetermining a size of the groomed channel to avoid spectralfragmentation.

In an alternative aspect of the same invention, there is provided anon-transitory storage medium with instructions for a computer toimplement performing all optical traffic grooming in an optical networkincluding providing distance-adaptive and fragmentation-awareall-optical traffic grooming that enables all-optical traffic groomingresponsive to provisioning of traffic demands in optical channels suchthat the spectrum required for guard bands is minimized, such thatnetwork fragmentation is minimized while ensuring transmission limitsover flexible-grid wavelength0-division multiplexed WDM networks arereached, the providing includes routing a groomed channel, selecting amodulation format for the groomed channel, selecting traffic demands tobe aggregated in the groomed channel, and determining a size of thegroomed channel to avoid spectral fragmentation.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1(a), (b) depicts fixed transmission channel spacing and flexibletransmission channel spacing to which the inventive method is directed.

FIG. 2 is a diagram depicting a genetic encoding in accordance with theinvention.

FIG. 3 is a diagram depicting an illustrative scenario, in accordancewith the invention.

FIG. 4 shows an exemplary computer for carrying out the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a novel computer implementedmethod, namely. Here, we design the first procedure, namelydistance-adaptive and fragmentation-aware all-optical traffic grooming(DFG) procedure, which addresses the all-optical traffic groomingproblem while considering the transmission reach constraints. The DFGprocedure provisions traffic demands in optical channels such that thespectrum requires for guard bands is minimized. The DFG procedureprovisions optical channels such that network fragmentation [APatel3] isminimized while ensuring the transmission reach constrains overflexible-grid WDM networks.

In the inventive DFG procedure, the traffic demands originated from thesame source node s are aggregated in a source set A_(s). The procedurefirst forms a source set A_(s) for each source node s in the network.The traffic demands from the same source set can potentially beaggregated into the same optical channel (referred to as optical tunnelor groomed channel). Let's denote a traffic demands j as R_(j)(s, d, b),where s is a source node, d is a destination node, and b is therequested data rate. The length (in terms of the number of hops) of agroomed channel supporting traffic demand j is denoted as L_(GC) ^(j),while the shortest path distance (in terms of the number of hops)between source s and destination d is denoted as L_(SP) ^(j). Thespectral efficiency of a groomed channel is denoted as E_(GC) based onthe modulation format and the distance traveled by the groomed channel.E_(SP) ^(j) denotes the optimal spectral efficiency of a traffic demandj if the demand is provisioned along the shortest path. A segment of agroomed channel in which a traffic demand j is groomed with othertraffic demands is referred to as a groomed segment of traffic demand j.The length (in terms of the number of hops) of traffic demand j'sgroomed segment is denoted as L_(GS) ^(j). The spectrum required for aguard band is denoted as W GHz.

All optical traffic grooming brings spectral gain due to the guard bandsavings in the groomed segments of optical channels. On the other hand,it may cause spectral loss due to the selection of sub-optimal routesand modulation formats while meeting the transmission reach requirementsof other members within the groomed channel. The spectral gain pertraffic demand obtained through all-optical traffic grooming is definedas follows:

$\begin{matrix}{G_{j} = {\left( {2 \times W \times L_{GS}^{j}} \right) - \left( {\left\lbrack \frac{b \times L_{GC}^{j}}{E_{GC}} \right\rbrack - \left\lbrack \frac{b \times L_{SP}^{j}}{E_{SP}^{j}} \right\rbrack} \right)}} & (1)\end{matrix}$

The DFG procedure first forms a source sets A_(s) by aggregating trafficdemands originating from the same source node s. The procedure selects asource set in which traffic demands request the maximum cumulative datarate. From the selected source set, the procedure selects a trafficdemand with the maximum shortest path distance between source anddestination nodes. An initial groomed channel containing just theselected traffic demand is first established. For the groomed channel, aroute is selected out of the K-shortest routes, and a spectral efficientmodulation format is selected which meets the transmission reachrequirement, such that spectrum for the groomed channel can beprovisioned at the lowest wavelength. Next, the procedure assigns a verylow cost to the links on which the groomed channel is routes, and a highcost is assigned to the rest of the links. Each traffic demand from thesame source set is routed over the minimum cost route one-by-one. If thelength of the found route of the selected traffic demand is smaller thanthe reach of the selected modulation format for the groomed channel, andif the spectral gain of the traffic demand based on the selected routeis positive, then the selected traffic demand can potentially be groomedwithin the groomed channel. In flexible grid network, optical spectrummay be fragmented due to the wavelength and spectral continuityconstraints. Such spectral fragmentation may lead to blocking of opticalchannels and reduce network throughput. To minimize spectralfragmentation in a network, the procedure forms groomed channels withspectral widths equivalent to the spectral fragments along the routeswith higher priority. Thus, the procedure checks weather the occupiedspectrum by the groomed channel is beyond the horizon of networkspectrum.

If the occupied spectrum by the groomed channel is higher than thehorizon of network spectrum, then the procedure selects the trafficdemands that can potentially be groomed. The groomed channel isaggregated with all these selected traffic demands, and these selectedtraffic demands are removed from the source set. Considering themodulation format of this new groomed channel to be the same as that ofthe previous groomed channel, and the line rate of this new groomedchannel to be at least the aggregated data rate of the groomed trafficdemands, the procedure finds new spectrum at the lowest wavelength onthe selected routes. The groomed channel is updated based on this newrouting and spectrum assignment solutions.

If the occupied spectrum by the groomed channel is lower than thehorizon of network spectrum, then the selected traffic demand along withthe previous groomed channel is considered as a potentially new groomedchannel. Considering the modulation format of this new groomed channelto be the same as that of the previous groomed channel, and the linerate of this new groomed channel to be at least the aggregated data rateof the groomed traffic demands, the procedure finds new spectrum at thelowest wavelength on the selected routes. If the new spectrum is stilllower that the spectral horizon of the network, then the selectedtraffic demand is removed from the source set, and the procedure updatesthe groomed channel by aggregating the selected traffic demand. Theroutes and spectrum assignment are also updated based on the foundsolutions. On the other hand, if the new spectrum is beyond the horizonof network spectrum, then the procedure does not groom the selectedtraffic demand and selects a new traffic demand from the source set.

After considering all traffic demands from the selected source set, theprocedure repeats the same procedure to establish a new groomed channelfor a source set which contains traffic demands with the maximumcumulative data rates.

The detailed steps of the procedure are described as follows.

101: The procedure forms a source set A_(s) for each source node s byaggregating traffic demands originating from the same source node s.

102: The procedure selects a source set with the maximum requestedcumulative data rate.

103: The procedure selects and removes a traffic demand with the maximumshortest path distance from the selected source set.

104: The procedure establishes a groomed channel by routing the selectedtraffic demand over one of the K-shortest routes and selecting thespectrum efficient modulation format such that spectrum for the channelcan be provisioned at the lowest wavelength.

105: The procedure assigns a very low cost to the links on which thegroomed channel is routed in the network, and assigns a higher cost tothe rest of the links.

106: The procedure selects a traffic demand from the source set that isnot yet considered.

107: The procedure finds a minimum cost route for the selected trafficdemand in the network.

108: The procedure checks two conditions for the selected trafficdemand; (1) Does the length of the found route smaller than the reach ofthe modulation format selected for the groomed channel, and (2) is thespectral gain of this traffic demand based on the found route ispositive? If both of these conditions hold true, then the procedurefollows Step 109, otherwise the procedure follows Step 106.

109: The procedure checks weather the maximum occupied spectrum by thegroomed channel is beyond the horizon of network spectrum? If themaximum occupied spectrum by the groomed channel is smaller or equal tothe horizon of network spectrum, then the procedure follows step 113,otherwise the procedure follows Step 110.

110: The procedure removes the traffic demand from the source set andconsiders it to be groomed.

111: The procedure checks weather all the traffic demands are consideredfrom the source set. If it is, then the procedure follows Step 112,otherwise the procedure repeats Step 106.

112: Finally, the procedure updates the groomed channel as follows. (1)The new line rate of the groomed channel must be at least the cumulativedata rate of all groomed traffic demands, (2) the modulation format ofthe groomed channel must remain the same, and (3) Along the selectedroutes of the groomed channel, reassign spectrum for this groomedchannel at the lowest wavelength.

113: The procedure considers a new groomed channel with a line rate thatis at least aggregated data rate of all groomed traffic demands so far.By considering the same modulation format as for the previously formedgroomed channel, the procedure finds spectrum for this new groomedchannel at the lowest wavelength along the selected routes.

114: The procedure again checks weather the maximum occupied spectrum bythe groomed channel is beyond the horizon of network spectrum. If it is,then the procedure follows Step 106, otherwise the procedure followsStep 115.

115: The procedure removes the traffic demand from the source set andconsiders it to be groomed.

116: The procedure updates the groomed channel based on the newlyselected line rate, routes, modulation format, and spectrum.

117: The procedure checks weather all the traffic demands are consideredfrom the source set. If it is, then the procedure follows Step 118,otherwise the procedure repeats Step 106.

118: The procedure checks weather all source sets are empty. If theyare, then the procedure terminates, otherwise the procedure repeats Step102.

The invention may be implemented in hardware, firmware or software, or acombination of the three. Preferably the invention is implemented in acomputer program executed on a programmable computer having a processor,a data storage system, volatile and non-volatile memory and/or storageelements, at least one input device and at least one output device. Moredetails are discussed in U.S. Pat. No. 8,380,557, the content of whichis incorporated by reference.

By way of example, a block diagram of a computer to support theinvention is discussed next in FIG. 7. The computer preferably includesa processor, random access memory (RAM), a program memory (preferably awritable read-only memory (ROM) such as a flash ROM) and an input/output(I/O) controller coupled by a CPU bus. The computer may optionallyinclude a hard drive controller which is coupled to a hard disk and CPUbus. Hard disk may be used for storing application programs, such as thepresent invention, and data. Alternatively, application programs may bestored in RAM or ROM. I/O controller is coupled by means of an I/O busto an I/O interface. I/O interface receives and transmits data in analogor digital form over communication links such as a serial link, localarea network, wireless link, and parallel link. Optionally, a display, akeyboard and a pointing device (mouse) may also be connected to I/O bus.Alternatively, separate connections (separate buses) may be used for I/Ointerface, display, keyboard and pointing device. Programmableprocessing system may be preprogrammed or it may be programmed (andreprogrammed) by downloading a program from another source (e.g., afloppy disk, CD-ROM, or another computer).

Each computer program is tangibly stored in a machine-readable storagemedia or device (e.g., program memory or magnetic disk) readable by ageneral or special purpose programmable computer, for configuring andcontrolling operation of a computer when the storage media or device isread by the computer to perform the procedures described herein. Theinventive system may also be considered to be embodied in acomputer-readable storage medium, configured with a computer program,where the storage medium so configured causes a computer to operate in aspecific and predefined manner to perform the functions describedherein.

From the foregoing the following can be appreciated from the inventivedistance-adaptive and fragmentation-aware all-optical traffic grooming(DFG): The DFG procedure improves the spectral efficiency of flexiblegrid networks. The DFG procedure decreases the connection blockingprobability in flexible grid networks. The DFG procedure is the firstpractical and complete control plane solution for all-optical trafficgrooming in flexible grid networks. The DFG procedure reduces the numberof required transponders in flexible grid network. The DFG procedurereduces the power consumption in flexible grid networks. The DFGprocedure increases the traffic carrying capacity of networks

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A computer implemented method for performing alloptical traffic grooming in an optical network, comprising: providingtraffic grooming that enables all-optical traffic grooming responsive toprovisioning of traffic demands in optical channels such that a spectrumrequired for guard bands over flexible-grid wavelength[0]-divisionmultiplexed WDM networks is reached, the providing comprising: routing agroomed channel, selecting a modulation format for the groomed channel,selecting traffic demands to be aggregated in the groomed channel; anddetermining a size of the groomed channel to avoid spectralfragmentation by: if a spectrum occupied by the groomed channel ishigher than a threshold of network spectrum, selecting traffic demandsto be groomed and aggregating the selected traffic demands, and removingselected traffic demands from a source set; considering a modulationformat of a new groomed channel to be the same as that of a previousgroomed channel, and a line rate of the new groomed channel to be atleast an aggregated data rate of groomed traffic demands, locating newspectrum at a lowest wavelength on selected routes and updating thegroomed channel based on a new routing and spectrum assignment.
 2. Themethod of claim 1, wherein the step of routing a groomed channelcomprises a groomed channel being first routed over one of a number ofshortest routes, and subsequently, traffic demands starting from samesource nodes overlap their routes with routes of an established groomedchannel.
 3. The method of claim 1, wherein the step of selecting amodulation format for the groomed channel comprises selecting amodulation format supporting a shortest path distance of traffic demandsoriginated from a same source node.
 4. The method of claim 1, whereinthe step of selecting traffic demands to be aggregated in the groomedchannel comprises a set of traffic demands originated from a same sourcenode being potentially aggregated in a groomed channel, eligibility foran aggregation being determined based on a route length, spectral gain,and availability of spectrum in an iterative manner.
 5. The method ofclaim 1, wherein the step of determining a size of the groomed channelto avoid spectral fragmentation comprises aggregating traffic demands ina groomed channel enabling a groomed channel to be provisioned below thethreshold of network spectrum.
 6. The method of claim 1, wherein thestep of routing a groomed channel comprises updating a groomed channelas follows: a new line rate of the groomed channel must be at least acumulative data rate of all groomed traffic demands, the modulationformat of the groomed channel must remain the same, and along selectedroutes of the groomed channel there is a reassignment of spectrum forthe groomed channel at a lowest wavelength.
 7. The method of claim 1,wherein the step of routing a groomed channel comprises considering anew groomed channel with a line rate that is at least an aggregated datarate of all groomed traffic demands, and considering the same modulationformat as for a previously groomed channel and finding for the newgroomed channel at least a lowest wavelength along selected opticalnetwork routes.
 8. A non-transitory storage medium with instructions fora computer to implement performing all optical traffic grooming in anoptical network comprising the following steps: providing trafficgrooming that enables all-optical traffic grooming responsive toprovisioning of traffic demands in optical channels such that a spectrumrequired for guard bands over flexible-grid wavelength[0]-divisionmultiplexed WDM networks is reached, the providing comprising: routing agroomed channel, selecting a modulation format for the groomed channel,selecting traffic demands to be aggregated in the groomed channel; anddetermining a size of the groomed channel to avoid spectralfragmentation by: if a spectrum occupied by the groomed channel ishigher than a threshold of network spectrum, selecting traffic demandsto be groomed and aggregating the selected traffic demands, and removingselected traffic demands from a source set; considering a modulationformat of a new groomed channel to be the same as that of a previousgroomed channel, and a line rate of the new groomed channel to be atleast an aggregated data rate of groomed traffic demands, locating newspectrum at a lowest wavelength on selected routes and updating thegroomed channel based on a new routing and spectrum assignment.
 9. Thenon-transitory storage medium of claim 8, wherein the step of routing agroomed channel comprises a groomed channel being first routed over oneof a number of shortest routes, and subsequently, traffic demandsstarting from same source nodes overlap their routes with routes of anestablished groomed channel.
 10. The non-transitory storage medium ofclaim 8, wherein the step of selecting a modulation format for thegroomed channel comprises selecting a modulation format supporting ashortest path distance of traffic demands originated from a same sourcenode.
 11. The non-transitory storage medium of claim 8, wherein the stepof selecting traffic demands to be aggregated in the groomed channelcomprises a set of traffic demands originated from a same source nodebeing potentially aggregated in a groomed channel, eligibility for anaggregation being determined based on a route length, spectral gain, andavailability of spectrum in an iterative manner.
 12. The non-transitorystorage medium of claim 8, wherein the step of determining a size of thegroomed channel to avoid spectral fragmentation comprises aggregatingtraffic demands in a groomed channel enabling a groomed channel to beprovisioned below the threshold of network spectrum.
 13. Thenon-transitory storage medium of claim 8, wherein the step of routing agroomed channel comprises updating a groomed channel as follows: a newline rate of the groomed channel must be at least a cumulative data rateof all groomed traffic demands, the modulation format of the groomedchannel must remain the same, and along selected routes of the groomedchannel there is a reassignment of spectrum for the groomed channel at alowest wavelength.
 14. The non-transitory storage medium of claim 8,wherein the step of routing a groomed channel comprises considering anew groomed channel with a line rate that is at least an aggregated datarate of all groomed traffic demands, and considering the same modulationformat as for a previously groomed channel and finding for the newgroomed channel at least a lowest wavelength along selected opticalnetwork routes.